The present invention relates to centrifugal casting and more particularly, to a chill preventing arrangement for use in centrifugal casting and method for preventing chill thereby.
Generally, in the centrifugal casting of metal, especially that of metal tubing or pipes and the like, there is employed a metal mold D or die as shown in FIG. 1 which normally includes a hollow cylindrical main body 1, an end plate E fitted into one end 1a or spigot portion of the main body 1 and having a central opening Ea substantially smaller in diameter than the internal diameter of the main body 1, and another end plate C releasably fitted into the other end 1b of the main body 1 and having a central opening Ca also smaller in diameter than the internal diameter of the main body 1 for preventing molten metal from running out of the ends 1a and 1b during casting. The molten metal m is poured into the mold main body 1 rotated by suitable means (not shown) at high speeds, via a spout S which enters the main body 1 through the central opening Ca in the end plate C, and the metal is distributed evenly over the entire inner surface of the main body 1 to form a hollow cylindrical or tubular casting as indicated at mc through centrifugal force. In the process of the centrifugal casting as described above, it is known to apply a coating composition including a parting agent onto the inner surface 1c or molding surface of the mold main body 1 prior to pouring the molten metal m into the mold 1, so as to form a refractory coating or lining (not shown) on such molding surface 1c for protecting the mold D from fusing by the heat of the molten metal m, and also for preventing the metal m from excessively rapid cooling which will give rise to formation of undesirable chills in the resultant castings. Such coating composition is normally sprayed, through a nozzle (not shown) mounted at one end of a supply pipe or applicator lance (not shown), onto the molding surface 1c of the rotating mold D in a direction perpendicular to or somewhat inclined to the molding surface 1c as the applicator lance advances horizontally into the hollow interior of the mold main body 1.
In the conventional arrangement as described above, known as the one coating-one casting method wherein the coating is renewed at each casting, however, it is difficult to sufficiently apply the coating composition onto the inner surface Eb of the end plate E whose surface is directed at right angles to the molding surface 1c whether the coating composition is sprayed onto the molding surface 1c in a direction perpendicular or rather inclined thereto, since the spraying is mainly directed toward the molding surface 1c, thus resulting in the formation of chills particularly at the corresponding end or spigot portion of the resultant casting which contacts the inner surface Eb of the end plate E due to rapid cooling imparted by plate E. Although the drawbacks as described above may be overcome by applying the coating composition separately onto the inner surface Eb of the end plate E at each casting, such a procedure is actually impractical, not only complicating the working process, but also resulting in reduction of productivity to a large extent. Accordingly, it is naturally required that the coating for the inner surface Eb of the end plate E, if to be formed, should be of a durable nature.
In order to meet the above requirements, there have conventionally been proposed various countermeasures wherein refractory material mainly of molten silica embedded in grooves formed in the inner surface Eb of the end plate E is calcined or wherein durable coating of known caking agents, for example, of phosphate, soluble glass and the like is applied onto the inner surface Eb or in which refractory ceramic material is applied through flame spraying onto the surface Eb to a thickness of 0.45 to 0.7 mm. Each of such countermeasures, however, has its weak point either in durability of the coating or in chill prevention effect, thus there being none which fully meets the desired requirements.